1. Field of the Invention
The present invention relates to a sealed battery, and more particularly to a sealed battery equipped with a mechanism that interrupts an electric current when the internal pressure of the battery case rises above a predetermined pressure.
Note that this application claims priority under the Paris Convention based on Japanese Patent Application No. 2012-015981, filed on Jan. 27, 2012, the entire contents of which are incorporated into this application by reference.
2. Description of the Related Art
Lithium ion secondary batteries, nickel hydride batteries and other secondary batteries have recently gained importance as power sources for vehicles that use electricity as drive power, or power sources installed in personal computers, portable terminals, and other electric devices. Such secondary batteries typically have a sealed structure (sealed batteries) in which a positive electrode and a negative electrode are sealed inside a battery case. Such sealed batteries are typically used while being controlled to a predetermined voltage range (for example, from 3.0 V to 4.2 V), and it can be supposed that where an abnormally high current is supplied to the battery, for example, due to malfunction, the predetermined voltage is exceeded and an overcharged state is assumed. During such overcharge, the electrolytic solution can be decomposed and gases can be generated inside the battery case, or the temperature inside the battery can rise due to heat generation in the active material. Accordingly, a battery provided with a mechanism that interrupts the electric current when the overcharge state is detected on the basis of battery temperature or pressure inside the battery (current interrupt mechanism, that is also called current interrupt device: CID) with the object of resolving the above-described problem has been suggested (see, for example, Japanese Patent Application Publication No. 2010-212034).
The current interrupt mechanism is provided, for example, in a conductive path between an outer connection terminal in a sealed battery (typically, a positive electrode outer connection terminal) and an electrode body accommodated inside the sealed battery. The current interrupt mechanism generally can be integrated with a sealing plate serving as the lid of the battery case of the sealed battery, with consideration for battery configuration and assembling ability.
For example, the current interrupt mechanism is provided on the inner side of the battery with respect to the sealing plate between the sealing plate and the electrode body. The current interrupt mechanism is essentially constituted by an inversion plate and a collector. The inversion plate is a member that is electrically connected to the connection terminal and configured such that an inversion section of the inversion plate is displaced and deformed outward of the battery when the pressure inside the battery rises. Further, the collector is electrically connected to the electrode body accommodated in the battery case and has an easily breakable section that is easily broken when predetermined stresses act thereupon. The inversion plate and the collector are usually joined together at the inversion section and the easily breakable section. However, when the pressure inside the battery rises and the inversion plate deforms in the overcurrent state, the easily breakable section of the collector breaks down and separates from the collector, thereby interrupting the conductive path of the inversion plate and the collector.
However, in the sealed battery equipped with such current interrupt mechanism, after the current interrupt mechanism has been actuated during the overcurrent, a spark is generated between the inversion plate and the collector and a pulse-shaped conduction occurs. A voltage recovery effect (residual voltage is present) is sometimes observed after the current interrupt mechanism is actuated.
For example, when the operation of the battery is managed by a control system, an abnormality in the battery can be detected by the voltage dropping to zero when the current is interrupted. Therefore, where such a conduction caused by a spark discharge occurs or a residual voltage is present after the current has been interrupted, the control system does not detect the battery abnormality and the system cannot be rapidly stopped.